Groove man,
          
          One more - your customer wants you to construct the 
          equivalent of a coax style shielded via from top to bottom 
          on a pcb???  Center conductor with a surrounding shield from 
          one side of the board to the other???
          
          Are they working with digital signals?  
          If so what are the edge rates?  
          They going from 20% - 80% rise time, 10%-90% rise time???
          Microseconds, nanoseconds, picoseconds???
          
          Did I interpret you message right?
          
          It sounds like they are imposing too much design 
          responsibility on you.  
          
          Like the seperation of traces stuff we all got into a little 
          while ago.  After talking with a couple of over-worked 
          underpaid talented pc board people late on a Saturday 
          afternoon, it occurred to me that alot of the criteria for 
          pc board design is OWNED by the designer of the circuit.  
          The one who gives you the schematic.  Not you unless that's 
          what you've agreed to.  
          
          And like you allude to in your message, when you (The Groove 
          man) are forced to start getting tutored in high freq RF or 
          microwave theory, its time to force the issue back onto the 
          customer (me being one of those people).  When someone 
          designs a circuit, its critical they understand what the pc 
          fabricators are going to do.
          
          I know I've gone way off track here, but, the bottom line is 
          they sound like they don't know what they're doing if they 
          are forcing this kind of thing on you.  Accomadating as you 
          are and as qualified as you are, there comes a time when pc 
          design should stay away from electrical design.
          
          There's my two cents.  I'll help anyway I can.
          
          Doug


______________________________ Reply Separator _________________________________
Subject: Re: FAB: RFI/EMI Vias
Author:  [log in to unmask] at internet-mail
Date:    5/23/96 8:25 PM


          
          Groove man,
          
          I would first ask: Does the customer want controlled 
          impedences on the board?  (I'm assuming they do...)
          
          Doug
          
          
______________________________ Reply Separator _________________________________
Subject: FAB: RFI/EMI Vias
Author:  [log in to unmask] at internet-mail 
Date:    5/23/96 5:46 PM
          
          
          
        I have a customer who has asked me if I know about shielding vias.
     I don't know much about these. All I know is that the size of the PTH 
     and the distance apart are based, somehow, on what frequency the 
     logic (PCB) is operating at. (Yessss?)
          
        Now I don't have IEEE text books anywhere near this facility. 
     I'm a simple fabricator. Can someone who's savvy with RF <or even 
     Microwave> design give me some pointers to what kind of formulas are 
     used to determine this shield via barrier technique.
          
          
     Thanks in advance for any and all replies.
          
     Groovy